Known food product tubular heat exchangers have a tube plate at each end of an elongated and typically cylindrical housing (shell) with a plurality of densely packed axial tubes extending between the two tube plates as a tube bundle. The ends of the tubes are received in corresponding through going holes in respective tube plates. During manufacturing of the heat exchanger the ends of the tubes are inserted into the holes and with a relatively tight fit and this relatively tight fit can be increased by rolling the inner side of the tubes so that the tube wall becomes thinner in the rolled area thereby tries to increase its diameter which causes the outer surface of the rolled tube area to be pressed against wall of the hole in the tube plate. Rolling is only applied in the end portion of the tube that is received inside a hole in the tube plate. Thereafter, the end of the tube is welded to the tube plate at the outer side of the tube. This procedure gives a strong connection that is satisfactory in various aspects such as production costs, reliability and preventing leakage of liquid from the interior of the cylindrical housing.
However, in the field of hygienic heat exchangers, i.e. heat exchangers that are suitable for use with liquid food products and that come in direct contact with liquid food products it is of utmost importance to avoid sharp corners, crevices, fissures, pockets or other forms of recesses are difficult to rinse and sterilize and where food rests can remain thus risking that microorganisms start to flourish.
The rolled joint with the weld at the outer side of the tube plates in the known heat exchangers (as shown in FIG. 6) does not live up to the hygienic requirements because it leaves crevices between the outer surface of the tube and the inner surface of the holes of the tube plate and it leaves a sharp corner 26 at the transition between the inner side of the tube plate and the outer surface of the tubes. Therefore, in these type of heat exchangers food products can only be used in the lumen of the tubes and not in the interior of the elongated housing.